An important parameter for the characterization of particulate substances is density. Measuring individual particle density becomes problematic, however, as particle size decreases. While optical and other measurement devices exist to determine overall sample sizes or volumes, these devices have difficulty measuring individual particle sizes. Moreover, measurement techniques often obtain only aggregate particle sizes, allowing at best an estimate or average of individual particle sizes. Obtaining an individual particle mass is also problematic, which in turn makes obtaining particle density problematic. Microbalances exist to obtain individual particle masses, but they are relatively costly and slow, often taking minutes to obtain the mass of even a single particle. Mercury pycnometery is often used to determine density of small particles, but can only obtain an average particle density. It cannot produce a histogram of individual particle densities. It also requires several grams of sample material, is labor intensive, and uses mercury, a hazardous substance.